(1) Field of the Invention
The present invention relates to an adjustment mechanism for adjusting the height of a work surface of a workstation. In particular, the present invention relates to an adjustment mechanism which uses rotation of a threaded member to adjust the height of the work surface. The threaded member is rotated by a handle through an operating mechanism having a series of sprockets and/or gears. The varying diameters of the gears allows the threaded member to rotate at a faster rate than the rate the handle is rotated. A spring is used to compensate for a load on the work surface and to allow the user to rotate the handle using less force.
(2) Description of the Related Art
The related art has shown various adjustable height workstations which use a rotating, threaded member and a stationary nut to adjust the height of the table or workstation. Illustrative are U.S. Pat. No. 1,943,280 to Arnold; U.S. Pat. No. 5,022,327 to Solomon; U.S. Pat. No. 5,447,099 to Adams et al; U.S. Pat. No. 5,685,510 to Francis; U.S. Pat. No. 5,845,590 to Seidel; U.S. Pat. No. 5,890,438 to Francis; and U.S. Pat. No. 5,941,182 to Greene.
Arnold describes a table having four adjustable legs. Each leg contains an adjustment mechanism which includes a screw and a stationary nut. A sprocket is mounted at the end of each screw. The sprockets of all four adjustment mechanisms are connected together by a chain. The chain passes about a drive sprocket which is mounted on a crank or handle. When the handle is rotated, the drive sprocket rotates which rotates the sprockets and screw of each adjustment mechanism.
Solomon describes an adjustable overbed table. A rotatable screw shaft is used to adjust the table. A crank handle is attached to bevel gears which rotate bevel gears on the end of the rotatable screw shaft.
Adams et al describes a height adjustment mechanism for tables. The drive means for the mechanism comprises a gear box, a jack screw and a jack nut with a crank for rotating the jack screw by means of a pair of bevel gears. One of the bevel gears is secured to the end of the jack screw.
Francis '510 and '586 describe a height adjustment system which includes a work-top member supported by a plurality of height adjustable legs. The legs have a stationary first leg part and a movable second leg part. A rotatable shaft extends vertically within the second leg part and has an upper portion and a lower portion. The lower portion is in the form of a screw. A pair of half nuts are positioned within the second leg part and act to position the screw within the second leg part. Vertical movement of the second leg part is also guided by at least one (1) linear bearing spaced between the first and second leg parts. The upper portion of the rotatable shaft is housed within a tubular member. A compression spring may be provided around the tubular member within the second leg part. The compression spring is retained between the lower part of the gear box housing and the base plate at the lower end of the first leg part. The compression spring is not rotatable and is fully supported within the second leg part to prevent buckling of the first leg part. The compression spring can compensate for external loads in the leg. The second leg part is secured at the upper end to the right angle gear box. The gear box includes a crown gear mounted on the upper end of the vertical shaft and a pinion gear engageable with the crown gear. The pinion gear is mounted on the end of a rotatable horizontal shaft which extends in a horizontal direction out of the gear box. The horizontal shaft is rotated by a drive mechanism comprising a winding mechanism including a rotatable drive shaft linked by universal joints and a first rotatable transmission member to a drive shaft. The drive shaft is connected to a rotatable drive transmission member which is connected to the horizontal shaft. A retractable handle is connected to the drive shaft for operating the winding mechanism. When the screw is rotated, the second leg part, gear box and work-top member move vertically relative to the first leg part.
Seidel describes an adjustable height table assembly. The base assembly includes a housing with a vertical leg extending upward and attached to the table top and movable within the housing. The housing also includes a pair of vertical guide members spaced from each other with a slide assembly slidably mounted to the guide members. The vertical leg is fixably mounted to the slide assembly. The vertical adjustment mechanism for the assembly includes a rotatable screw extending through a passage defined by the vertical leg. A tubular member is mounted within the housing between the vertical guide members, and receives the lower portion of the threaded member. A fixed nut is mounted toward the upper end of the tubular member and is threadably engaged with the threads of the screw. The table top support further includes an arm to which the table top is secured. The arm defines an axial passage, which is in communication with the passage formed in the vertical leg through which the screw extends. A driven sprocket is mounted to the screw toward its upper end, and a drive sprocket is rotatably mounted to the arm below the table top. A chain is engaged with the drive sprocket and with the driven sprocket, and a manually operable crank provides rotation of the drive sprocket, which is transferred through the chain and the driven sprocket to impart rotation to the screw and to thereby adjust the height of the table top.
Greene describes a vertically adjustable table which is adjustable using a crank handle. The leg assemblies include a stationary part and a movable part. The lifting mechanism comprises a ball screw and a ball nut. The ball nut is rigidly affixed to the stationary part of the leg assembly and the ball screw rotates in the ball nut. The table top is raised or lowered depending on the direction of rotation of the screw. The table uses a pulley and cable arrangement to ensure that the table raises and lowers in a level manner which obviating the need for a chain and sprocket. A miter gear set is used to convert horizontal torque applied by the user on the handle to the vertical torque needed to rotate the ball screw. The gear box mechanism is securely attached to a bracket which is secured to the movable portion of the leg assembly and to the underside of the table. The gear box mechanism is also securely attached to the ball screw.
Also of interest are U.S. Pat. No. 4,635,492 to Uebelhart; U.S. Pat. No. 5,088,421 to Beckstead and U.S. Pat. No. 5,282,593 to Fast which show the use of a motor to rotate the threaded member to adjust the height of a table or workstation.
There remains the need for an adjustment mechanism for use in adjusting the height of a work surface of a workstation which is manually operated by a handle which allows for fewer rotations of the handle by the user to obtain the required height adjustment and which uses a spring to compensate for a load on the work surface.